REPTILIA. CROCODILIA. 211 



abdominal splint ribs (fig. 46, 4) occur. The sternum is carti- 

 laginous, and both it and the shoulder-girdle are very simple. 

 The precoracoid is represented by merely a small process on 

 the coracoid, while the clavicles are absent, except in the 

 Parasuchia. In the pelvis (fig. 49) there is a large ilium, and 

 an ischium meeting its fellow in a ventral symphysis ; these 

 two bones form almost the whole of the acetabulum. In 

 front of the acetabulum, in the Eusuchia, projects a bone 

 which is generally called the pubis, but is in reality rather 

 an epipubis (fig. 49, 4), the true pubis being probably repre- 

 sented by a fourth element which remains cartilaginous for 

 some time, and later on ossifies and attaches itself to the 

 ischium. The limbs are small in proportion to the size of the 

 body, and are adapted for swimming or for shuffling along the 

 ground ; they are plantigrade and the bones are all solid. 

 In living forms the anterior limbs have five digits and the 

 posterior four, the fifth being represented only by a short 

 metatarsal. The first three digits in each case are clawed. 

 The calcaneum has a large back ward ly-projecting process. 



The order Crocodilia may be subdivided into two sub- 

 orders. 



Suborder (1). PARASUCHIA. 



The vertebral centra are flat or biconcave. The pre- 

 maxillae are very large, and the nares are separated, and 

 placed far back. The posterior narial openings lie compara- 

 tively far forward between the anterior extremities of the 

 palatines. 



The palatines and pterygoids do not form a secondary 

 palate. The supratemporal fossae are small, and open poste- 

 riorly, the lateral temporal fossae are very large. The parietals 

 and frontals are paired. Clavicles are present. The best 

 known and most important genus of these extinct crocodiles 

 is Belodon. 



142 



